A facility characteristic of the premises broadcasting device used for public purposes and a short accident of a distribution line of a loudspeaker on a user environment cause a very serious problem.
Disconnection does not influence the same or a plurality of systems of normal loudspeaker loads, but in the case of short, a problem is, in a lump, caused in the normal loudspeaker load of the entirety of the same system due to a result such as broadcasting discontinuation and subsequently, the short may become a cause of damage of an output amplifier of a premises broadcasting device.
In particular, sound transmission stop primarily occurs and a side effect of the damage of the output amplifier secondarily occurs in a theatre, a rally place, an educational institution, and using multiple loudspeaker loads for public sound transmission.
Meanwhile, in the case of a multi-family house or a multi-layered apartment, since broadcasting stop of all houses due to the short in occurrence of an emergency situation or in the event of fire causes property loss and life damage, a short accident of the loudspeaker load including the distribution line of the loudspeaker is particularly specified and defined based on the Fire Safety Standards Act of emergency broadcast equipment in most countries at present.
In addition, conventional general background technology considering the short of the loudspeaker distribution line or the loudspeaker load of the premises broadcasting device may be largely divided into two types described below.
A first type background technology which is disclosed in Patent Registration No. 0661401 is a technology that protects the output amplifier by interrupting input and output signals of the output amplifier in the short and cannot avoid an entire broadcasting stop state and just protects the output amplifier.
A second type background technology disclosed in Patent Registration No. 0998516 is a technology that limits load short current approximately with a load current value corresponding to one system insertion resistance value in the short of the load under a condition to serially insert resistance of the same capacity as a load value for each corresponding load into each loudspeaker load system.
However, in the former case, as a countermeasure for protecting the amplifier or the speaker in the short, a function of a speaker or an amplifier of the loudspeaker stops by interrupting an input signal and an output signal as an amplifier protecting means, and as a result, a systematic condition that cannot prevent a broadcasting stop situation is provided in houses of the same system that accommodate normal loads, in which the short accident does not occur.
For example, as illustrated in FIG. 1, in the case of a short of a house loudspeaker group 3, since all loudspeaker distribution lines 4 and loads are connected in parallel through a speaker selection switch 2, whole broadcasting cannot but stop by an output interruption unit of an amplifier and speaker protection circuit 1 even though an input signal is present in a signal input terminal 5.
It can be seen that the Patent Registration No. 0661401 is used not for a house requiring in-system loudspeaker broadcasting but for protecting the amplifier and the speaker in an individual short through an electrical system of a signal and matters associated therewith is specified even in prior art of the registered patent.
In particular, the Patent Registration No. 0661401 mentions seriousness of the short accident of the loudspeaker distribution line due to the facility characteristic of the premises broadcasting device, but the final protection purpose is to protect the amplifier and the speaker and it can be seen that in the case where the corresponding device detects the short accident when the short accident occurs, an amplifier input signal is attenuated by a relay RY2 in a circuit diagram illustrated in FIG. 3 in a publication of the registered patent and an OUT signal of a relay RY1 is interrupted.
Therefore, an attenuation signal is input into the amplifier to operate weakly when the short is detected, but since a short or an abnormal output signal is interrupted by the relay RY1, the amplifier and the speaker are protected while broadcasting stops.
Accordingly, due to disconnection of an amplifier output signal of the corresponding broadcasting device, the broadcasting stops in the shorted house loudspeaker and normal house loudspeakers of the same system connected in parallel, and as a result, a public goal such as emergency broadcasting fire safety standards, and the like cannot be achieved.
Moreover, since the speaker and an output control unit are configured as a single circuit, it is apparent that a goal of the background art to be achieved is to protect apparatuses of the broadcasting device, and as a result, whole broadcasting such as sound transmission, announcement, or evacuation guidance broadcasting through the same system of loudspeaker distribution line cannot avoid the interruption situation when the short accident occurs in a house load such as a theatre, a rally place, an educational institution, or a multi-family house, or a multi-layered apartment using multiple loudspeaker loads for public sound transmission.
Meanwhile, the latter case discloses an amplifier protection device of a premises broadcasting circuit and according to the disclosed publication, there is a primary purpose that an output of the amplifier to other speaker is normally achieved by effective protecting the amplifier even though the short occurs in the speakers and states of the distribution lines of the speakers can be very easily monitored in real time to discover a problem in broadcasting circuit in the early stage.
That is, the amplifier protection device of the premises broadcasting circuit is provided in which resistance corresponding to an impedance value of the speaker which is a final load is added, however, inserted in series, and as a result, when the short occurs in the distribution line (load), the amplifier is not in a short state but the inserted resistance becomes an electrical load. Therefore, referring to FIG. 2, in regard to a circuit element additionally applied against the occurrence of the short, one R1, R2, or ˜Rn is provided, N speaker selection switches 2 (switch 1, switch 2, and switch n) are universal mechanical contact passive switches, an LED level meter which is a component of the amplifier and speaker protection circuit 1 is used for visually determining the short, a final parallel connection is provided, in which all load distribution lines or the speaker selection switch 2 and the resistances R1, R2, and ˜Rn are connected in series when the short occurs in one house (house 1) of the house loudspeaker group 3 or when an individual short occurs in the loudspeaker distribution lines 4, and as a result, the load resistances R1, R2, and ˜Rn becomes corresponding loads regardless of an input signal of the input signal terminal 5 of the amplifier to protect the amplifier from overload short current and enable broadcasting transmission to residual houses (house 2 to house n) and herein, the following problems consequently occur.
First, the device disclosed in the Patent Registration No. 0998516 has a limit in that the device cannot autonomously read the short state or perform a confrontation action.
For example, when the short occurs in the speaker (including the distribution lines), as a load impedance value decreased to ½, and as a result, a load which is twice larger than the load in the normal state and since there is a structure in which a selection switch is fixed, the device cannot autonomously electrically open or separate the short distribution line, a person needs to decide whether to turn off the switch by a hand or separately configuring a relay using an additional device by reading whether it is abnormal through visually viewing a level meter.
However, in respect to the characteristic of the audio signal, a real-time change of the amplitude is large, a periodic change of the signal is also rapid and frequent, and the signal is irregularly changed, a short situation needs to be determined by visually distinguishing an LED level meter display difference which moves in response to the twice change of the load. Therefore, the possibility is not easy by unspecific majority having a common sense and further, there is a precondition that the person needs to monitor the level meter at normal times, and as a result, there is almost no effectiveness.
Second, Joule's heat(Q=0.24 I2Rt) which is in proportion to the square of the load current and the corresponding resistance and time is generated due to insertion of resistance into speaker lines of all houses.
That is, in the case of a school cited by Patent Registration No. 0998516, individual classroom may have relatively small power (3 W to 10 W), but a plurality of classrooms (2-4) may be provided, and as a result, the classrooms may have 12 [W] to 40 [W] and a special room, a hallway, a playground may have hundreds of watts [W]. Therefore, there is a signal volume increase element and a fire risk element due to heat dissipation in consuming power similarly to the speaker, that is, heat dissipation processing.
Moreover, since the number of speaker loads is not one but multiple as many as all houses, a generated heat amount increases according to the sum-up of loads, a fire risk burden increases as much, and output power of the amplifier corresponding to heat dissipation of a dummy load causes additional loss and in the case of additional loss by the corresponding output power loss, power of approximately 1.2 times is wasted in a D-class amplifier and power corresponding to approximately twice of the output power is wasted in an AB-class amplifier.
Third, while a short protection operating function by the process is established, dummy load resistance having a capacity of 42[Ω] and 240 [W] is provided, which is the same as the speaker capacity and the output voltage of the amplifier needs to be twice larger than the standard (100 V) and an amplifier output capacity needs to also be twice (480 W) in order to normally use a universal 240 [W] speaker. That is, there is a condition in which the corresponding loss according to twice cannot be allowed.
Moreover, since voltage is twice while load impedance is half in the short, a capacity which the dummy load in an actual short needs to endure twice of the amplifier capacity that is, 960 [W] and before visually reading the LED level meter or turning off the switch due to a contact in a demand place, heat-resistant dummy load (resistance-1 to resistance-n) to endure the capacity needs to be naturally provided and the amplifier capacity requires general 4 times output power to endure the capacity, and as a result, there is a problem in that output setting is upward applied to 4 times in order to apply the amplifier to actual usage.
If it is premises that amplifier voltage and output do not increase, since total load impedance becomes twice due to synthetic impedance connected with the dummy load in series, there is a problem in that input power of the speaker cannot but decrease to ¼, and as a result, there is a negative effect in which remarkable volume decrease occurs together with significant loss. Therefore, it is inefficient and normal driving of the speaker device cannot be expected.
As a technology disclosed in amplifier and speaker protection circuits of two types of broadcasting devices or an amplifier protection device of the premises broadcasting circuit, there is a limit in that the effectiveness deteriorates even though a broadcasting stop situation cannot be prevented or is applied.
Further, unlike the case of the short in the loudspeaker distribution line and the load of the premises broadcasting device, since a serial additional equivalent state is distributed in an electrical attribute of the short due to the distribution line resistance value and the impedance value, the distribution line resistance value and the impedance value are aggregated to an actual load amount value.
For that reason, there is a limit in an attempt to settle an overload, an abnormal state, and the short by measuring impedance of the load or the magnitude of load current and that is to say, when a configurational detailed element of the load of the premises broadcasting device is described, an added impedance value actually includes a required equivalent resistance component of the loudspeaker distribution line as an effective value (several Ω to tens of Ω) in serial at all times and there is a problem in that a case in which the state of the short cannot be clearly determined due to a distribution line resistance value of a predetermined size.
As one example, in a load having an impedance value of 8[Ω], when a resistance value of the distribution line to which a capacity of 1000 [W] is applied is 10[Ω], since an impedance value of a practical load is 18[Ω], even though the short occurs in both ends of the load, the impedance value is recognized as the load of 10[Ω] and the load capacity which is less than 1000 [W], and as a result, a detection protecting device in the related art of the audio amplifier is not recognized as an overload state.
As another example, in a universal premises broadcasting device having line voltage of 100 [V], an impedance value of a 500 [W] load is 20[Ω] and in the case where the synthetic load impedance value when an equivalent resistance value of the distribution line is 20[Ω] or more becomes 40[Ω] or more and the short occurs in a load terminal, since the synthetic load impedance value becomes just 20[Ω] due to the distribution line resistance value, the impedance value cannot be recognized as the normal load of 20[Ω].
As such, since an actual distribution line resistance value of the loudspeaker distribution line of the premises broadcasting device becomes an aggregate element of an impedance increase added to correspond to an actual load, a determination reference point of the abnormal state and the overload of the distribution line or the load cannot but fluctuate, and as a result, the abnormal state cannot be clearly settled with a fixed absolute value.
Further, since the audio signal itself has a characteristic in that a voltage value of an effective output is progressed according to the time while continuously irregularly fluctuating, it is difficult to calculate an effective power value and even though an ideal average value is calculated, the abnormal state and the overload cannot be clearly concluded by concluding and defining the voltage value as the fixed value. For example, when 5 [W], 50 [W], 500 [W], or 5000 [W] is applied to the corresponding load, since the corresponding load may be the normal load, an addition function for abnormal load analysis cannot also a basic analyzing and processing function even though a converted specific load amount (value) becomes a predetermined reference value of the determination of the overload.